ABSTRACT
Rales of microbial cycling of inorganic and organic phosphate (P) compounds in aquatic environments can be measured by radioisotope and fluorescence methods. These measurements include uptake and regeneration of inorganic orthophosphate (Pi), enzymatic hydrolysis of specific components of the dissolved organic, and uptake of the released Pi. The advantages of the isotopic techniques are: very high sensitivity, because labelled substrates are available at tracer or near-tracer concentrations so adding label does not increase the overall substrate concentrations and labelled substrates are actual substrates. It also includes P-labelled organics allow the fate of the released Pi to be followed after hydrolysis and small samples can be rapidly batch-processed using multiplace filtration rigs. To measure enzymatic hydrolysis of organic P, radiolabel organic P compound is added to a water sample and incubated. Since the rates of most hydrolysis and uptake processes decline over a time course, it is not always clear how many and which time points to include in a regression.
